Method and apparatus for supporting handover from lte/eutran to gprs/geran

ABSTRACT

A method and apparatus for handover of a dual mode wireless transmit/receive unit (WTRU) from an LTE system to a GERAN system uses measurements of the LTE and GERAN frequencies and a decision by a source evolved Node B to perform the handover. A GERAN access procedure includes PS attach messages exchanged between the WTRU and the target base station controller and a target SGSN. Alternatively, the GERAN access procedure uses RAN mobility information messages exchanged by the WTRU and the target base station controller and a relocation detect message by the source evolved Node B.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application No.60/889,383, filed Feb. 12, 2007, which is incorporated by reference asif fully set forth.

FIELD OF INVENTION

This application is related to wireless communications.

BACKGROUND

There are different types of wireless communication systems. Forexample, some wireless communication systems include general packetradio service (GPRS), global system for mobile (GSM)/enhanced data ratesfor GSM evolution (EDGE) radio access network (GERAN), and the newlyintroduced long term evolution (LTE) evolved universal terrestrial radioaccess network (EUTRAN). LTE/EUTRAN system has a different physicallayer and a different architecture from those systems preceding it,i.e., GPRS, GERAN, or UTRAN.

When a Multi-mode mobile unit is traveling across the geographiccoverage of these different systems, it may need to be handed off fromone network to another. Since not all networks are identical, a methodfor supporting the handover between systems would be beneficial.

FIG. 1 shows an exemplary diagram of a system 100 including an LTEsystem architecture. The system 100 shows an LTE/EUTRAN 101 and itsevolved packet core 105 interworking with an existing GERAN 102, UTRAN103, and their GPRS Core 104. The LTE/EUTRAN 101 comprises an E-Node B(not shown) that is connected (S1) to an evolved packet core 105containing a mobility management entity/user plane entity (MME/UPE) 106and an inter AS anchor Gateway 107. The Evolved Packet Core 105 connects(S6) to a home subscriber service (HSS) 111, and connects (S7) to aPolicy and Charging Rules (PCRF) 112. The inter AS Anchor gateway 107connects (Gi) to Operator IP Servers (such as IMS, PSS) 110, connects(S2) to a Non-3GPP IP Access network 108, and connects (S2) to a WLAN3GPP IP Access network 109. The GPRS Core 104 comprises a Serving GPRSSupport Node (SGSN) (not shown) which is responsible for MobilityManagement, Access Procedures, and User Plane Control. The GPRS Core 104also comprises a Gateway GPRS Support Node (GGSN), where the network isconnected to external networks and other operator servers. The OperatorIP Servers 110 may include an IP Multimedia Service Subsystem (IMS)where VoIP and other multimedia services are controlled. The Non-3GPP IPaccess network 108 includes connections to other technologies that aredeveloped in other standard Forums such as 3GPP2 (CDMA2000) and WiMAX(IEEE 802.16 system). The WLAN 3GPP IP access network 109 has WLANsincorporated into 3GPP systems via interworking architecture defined in3GPP.

SUMMARY

A method and apparatus for supporting handover from an LTE/EUTRAN cellto a general packet radio service (GPRS)/global system for mobilecommunications (GSM)/enhanced data rates for GSM evolution (EDGE) radioaccess network (GERAN) cell. In one embodiment, a GERAN access procedureduring the handover includes sending a packet switched (PS) attachsignal. In another embodiment, the GERAN access procedure includes RANmobility information messages being exchanged between the WTRU and atarget base station controller (T-BSC).

BRIEF DESCRIPTION OF THE DRAWINGS

A more detailed understanding may be had from the following description,given by way of example in conjunction with the accompanying drawingswherein:

FIG. 1 shows an example of an LTE general network architecture;

FIG. 2 shows an initial state for handoff from an LTE system to aGPRS/GERAN system;

FIG. 3 shows a second state for handoff from an LTE system to aGPRS/GERAN system;

FIG. 4 shows a third state for handoff from an LTE system to aGPRS/GERAN system;

FIG. 5 shows a functional block diagram of a wireless transmit/receiveunit and a Node B;

FIGS. 6A, 6B, 6C show a signal flow diagram of a handover procedureincluding a packet switched (PS) handover signal; and

FIGS. 7A, 7B, 7C show a signal flow diagram of a handover procedureincluding a relocation detect from a source evolved Node-B (S-ENB) to atarget base station controller (T-BSC).

DETAILED DESCRIPTION

When referred to hereafter, the terminology “wireless transmit/receiveunit (WTRU)” includes but is not limited to a user equipment (UE), amobile station, a fixed or mobile subscriber unit, a pager, a cellulartelephone, a personal digital assistant (PDA), a computer, or any othertype of user device capable of operating in a wireless environment. Whenreferred to hereafter, the terminology “base station” includes but isnot limited to a Node-B, a site controller, an access point (AP), or anyother type of interfacing device capable of operating in a wirelessenvironment.

FIGS. 2-4 show examples of three states of traffic paths and tunnelsestablished between network entities during a handover of a WTRU from anLTE network to a GERAN network. In FIG. 2, an initial state 200 is shownfor a mobile WTRU 201 moving from an LTE network cell designated aslocal area LA2/Routing Area RA2, to a GERAN system LA1/RA1. The cellsbelonging to GERAN systems may constitute different LocationArea/Routing Area (LA1/RA1) from those belonging to LTE based cells(LA2/RA2). In certain deployments, although GERAN cells may beco-located with GERAN cells, these cells will remain under differentLA/RA configuration due to the difference between the two systemarchitectures. Other WTRUs 254, 255 are shown camped on the cellLA2/RA2, and WTRUs 251, 252 are camped on the cell LA1/RA1. The WTRU iscurrently connected to an access gateway 211 via a source Evolved Node B(ENB) 222, where tunnels 215 and 216 are established for the user dataplane. Source mobility management entity (MME) 221 controls mobility andhandles user control plane traffic on tunnels 217 and 218. User controlplane traffic is connected on tunnel 219 between the source ENB 222 andthe WTRU 201. The target GERAN system comprises a target SGSN 231, atarget base station controller (BSC) 232, and a target mobile servicesswitching center/visitor location register (MSC/VLR) entity 233.

FIG. 3 shows an optional second state 300 for tunneling of networkentities during the handover of the WTRU 201 from the LTE network cellLA2/RA2 to the GERAN cell LA1/RA1. The WTRU 201 is now migrated to theGERAN cell LA1/RA1.

An optional tunnel 225 may be created between the target BSC 232 of theGERAN system and the source ENB 222. The tunnel 225 may be used totemporarily forward the current pending data transfer between GERANsystem and the WTRU via E-Node B while a new connection between theEvolved Core Network 105 and the GPRS Core 104 (i.e., while the backboneprocedures to switch traffic is completed). This will ensure that nodata is lost during transition. A system operator may choose not toimplement this step and go to a complete transition case where noconnection is established between the GERAN BSC 232 and ENB 222. In sucha case, forwarding of data occurs at higher layers, between the two corenetworks on S3 and S4 connections. The user data plane and control planetraffic is carried to the WTRU 201 across the tunnels 235 and 236,respectively.

FIG. 4 state 400 for tunneling of network entities during the handoverof the WTRU 201 from the LTE network cell LA2/RA2 to the GERAN cellLA1/RA1. As shown in FIG. 4, the traffic switching has occurred in theupper layers such that the GERAN system is now is the network source foruser traffic, as shown by GGSN 411. The WTRU 201 is now connected to theGERAN system GGSN 411 via the Target SGSN 231, and the target BSC 232,on user data plane and control plane tunnels 415, 416 and 417,respectively.

FIG. 5 is a functional block diagram of a WTRU 510 and a Node B 520. Asshown in FIG. 5, the WTRU 510 is in communication with the Node B 520and both are configured to support handover from GPRS/GERAN toLTE/EUTRAN.

In addition to the components that may be found in a typical WTRU, theWTRU 510 includes a processor 515, a receiver 516, a transmitter 517,and an antenna 518. The processor 515 is configured to support handoverfrom GPRS/GERAN to LTE/EUTRAN. The receiver 516 and the transmitter 517are in communication with the processor 515. The antenna 518 is incommunication with both the receiver 516 and the transmitter 517 tofacilitate the transmission and reception of wireless data. Theprocessor 515, receiver 516, transmitter 517, and antenna 518 may beconfigured as a GPRS/GERAN radio transceiver, or configured as anLTE/EUTRAN radio transceiver. Also, although only one processor,receiver, transmitter, and antenna is shown, it should be noted thatmultiple processors, receivers, transmitters, and antennas may beincluded in the WTRU 510, whereby different groupings of processors,receivers, transmitters, and antennas operate in different modes, (e.g.,GPRS/GERAN transceiver or LTE/EUTRAN transceiver).

In addition to the components that may be found in a typical Node B, theNode B 520 includes a processor 525, a receiver 526, a transmitter 527,and an antenna 528. The processor 525 is configured to support handoverfrom LTE/EUTRAN to GERAN. The receiver 526 and the transmitter 527 arein communication with the processor 525. The antenna 528 is incommunication with both the receiver 526 and the transmitter 527 tofacilitate the transmission and reception of wireless data.

In a first embodiment, GERAN access procedures include packet switched(PS) attach signals between the LTE transceiver of the WTRU 510. FIG. 6shows exemplary signal diagram of a handover procedure 600 for thisembodiment. While the following signals are shown in FIG. 6 anddescribed in a particular sequence, the signals may occur in variationsto the sequence in accordance with this embodiment.

In the signal diagram of FIG. 6, signals are exchanged among: a dualmode LTE/GERAN WTRU having an LTE transceiver and a GERAN transceiver,each transceiver comprising a receiver and a transmitter; a sourcee-Node B (S-ENB); a target BSC (T-BSC); a source LTE-MME; a target SGSN;and an LTE UPE/Gateway. The dual mode WTRU in this example includes anLTE and GERAN transceiver.

As shown in FIG. 6, user downlink (DL) and uplink (UL) traffic 601 a,601 b is exchanged between the WTRU LTE transceiver, the S-ENB and theLTE UPE/Gateway. The WTRU LTE transceiver performs measurements 605 onLTE frequencies and GERAN frequencies, and transmits a GERAN measurementreport signal 606 to the S-ENB. The WTRU may receive a list of differentradio access technologies, including GERAN, from the S-ENB to identifythe types of frequency measurements to undertake. Intersystem Handover607 is initiated by the S-ENB, which makes the handover decision basedon the measurement report 606, with GERAN being the target. A relocationrequest signal 608, containing the source cell ID and the target cellID, is transmitted from the S-ENB to the source MME. The source MMEmakes a determination 609 of the target system cell ID and the SGSN IDby mapping the target cell ID (GERAN) to an SGSN IP address. The sourceMME forwards the relocation request 610 to the target SGSN, including aninternational mobile subscriber identity (IMSI), source cell ID andtarget cell ID.

The target SGSN performs a determination 611 of the target BSC ID, andrequests the user profile and context if it was not included insignaling message 610. The target SGSN sends a handover request signal612 to the T-BSC, including the cell ID, SGSN ID, and the internationalmobile subscriber identity/temporary mobile subscriber identity(IMSI/TMSI). The T-BSC performs a determination 613 of channelavailability and initiates radio access bearer (RAB) establishment. TheT-BSC transmits a handoff request ACK 614, including the IMSI/TMSI, tothe Target SGSN. A user plane and control plane tunnel 615 isestablished between the T-BSC and the Target SGSN. The target SGSNcreates an MM state and SM state 616 to prepare for activating packetdata protocol (PDP) context information.

The target SGSN sends a relocation response 617 including an IMSI andSGSN ID, to the Source MME, which sends a relocation command signal 618,that includes the TMSI and target BSC ID to the S-ENB. A temporarytunnel 619 to the T-BSC is established by the S-ENB to forward user datato the T-BSC. A handover command 620 is transmitted from the source MMEto the S-ENB, and is forwarded to the WTRU LTE transceiver, whichrecognizes the target GERAN technology amongst others that may besupported, and an initiate/synch radio signal 621, including a targetchannel ID, is communicated to the WTRU GERAN transceiver. The GERANtransceiver sends an ACK signal 623. User data 622 is exchanged on thetemporary tunnel 619 between the S-ENB and the T-BSC. A handovercomplete signal 624 is sent from the WTRU LTE transceiver to the S-ENB.The T-BSC sends a relocation detect signal 625 to the target SGSN.

The GERAN access procedure includes a PS attach signal 626 transmittedfrom the WTRU GERAN transceiver to the T-BSC, which forwards the PSattach signal 627 to the target SGSN. A PS attach accepted signal 628 isreturned by the target SGSN to the T-BSC. The WTRU GERAN transceiver isconfigured to receive a PS attach Accept 629 from the T-BSC, and torespond with a PS attach accept ACK 630. The T-BSC forwards a PS attachaccept ACK signal 631 to the target SGSN.

The target SGSN performs an update 633 of the PDP context with the newSGSN TEID, and establishes a tunnel 634 with the LTE UPE/gateway for aGPRS tunneling protocol user plane and control plane (GTP-U and GTP-C).At this stage the user plane path is established for all PDP contextsbetween the WTRU GERAN transceiver, Target BSC, Target SGSN, and servinggateway. The switch of traffic 638 is complete from the source ENB tothe target SGSN. Between the WTRU GERAN transceiver and T-BSC, a tunnel632 is established for exchange of RAN information and RABestablishment, and user DL/UL traffic 635 is exchanged.

A handover complete signal 636 is sent from the target SGSN to thesource MME, which sends a release signal 639 to the S-ENB and an HOcomplete ACK 637 to the target SGSN. The S-ENB performs a release 640 ofits resources related to the WTRU, and stops forwarding data. A releaseACK 641 is transmitted from the S-ENB to the source MME, and user DL/ULGERAN traffic now flows on tunnel 642 between the WTRU GERAN transceiverand the target BSC, on tunnel 643 between the T-BSC and the target SGSN,and on tunnel 644 between the target SGSN and the GGSN gateway.

FIG. 7 shows a signaling diagram according to a second embodiment inwhich the GERAN access procedure includes a relocation detect signalfrom the source ENB and the target BSC, and RAN mobility informationsignals. In this embodiment, the signals are similar to the firstembodiment as shown in FIGS. 6A, 6B and 6C, except for the followingsignals which are used in lieu of the PS attach signals 626-631 excludedin this embodiment.

As shown in FIG. 7, a GERAN access procedure begins the handovercomplete signal 624. A relocation detect signal 725 is sent by the S-ENBto the T-BSC, and a relocation detect signal 726 is forwarded from theT-BSC to the target SGSN. RAN mobility information 727 is transmitted bythe T-BSC to the WTRU GERAN transceiver, which returns a RAN mobilityinformation ACK 728. The T-BSC sends a Relocation complete signal 729 tothe target SGSN.

As described in FIGS. 1-7 above, radio resources are prepared in thetarget 3GPP access system before the WTRU 510 is commanded by the source3GPP access system to change to the target 3GPP access system. A tunnelis established between the two radio access networks (RANs) (basicservice set (BSS)/basic service controller (BSC) and E-Node B) in orderto forward the data while the core network resources are assigned.

A control interface may exist in the core level between the 2G/3G SGSNand corresponding MME to exchange the mobility context and the sessioncontext of the Mobile. Additionally, the target system may providedirections to the WTRU as to the radio access requirements, such as theradio resource configuration, target cell system information, and thelike.

There is an intermediate state during handoff where the DL User planedata is sent from source system to the target system before the Userplane is switched directly to the target system in order to avoid theloss of user data, (e.g., by forwarding). Bi-casting may also be useduntil the 3GPP Anchor determines that it can send DL U-plane datadirectly to the target system.

Although features and elements are described above in particularcombinations, each feature or element can be used alone without theother features and elements or in various combinations with or withoutother features and elements. The methods or flow charts provided hereinmay be implemented in a computer program, software, or firmwareincorporated in a computer-readable storage medium for execution by ageneral purpose computer or a processor. Examples of computer-readablestorage mediums include a read only memory (ROM), a random access memory(RAM), a register, cache memory, semiconductor memory devices, magneticmedia such as internal hard disks and removable disks, magneto-opticalmedia, and optical media such as CD-ROM disks, and digital versatiledisks (DVDs).

Suitable processors include, by way of example, a general purposeprocessor, a special purpose processor, a conventional processor, adigital signal processor (DSP), a plurality of microprocessors, one ormore microprocessors in association with a DSP core, a controller, amicrocontroller, Application Specific Integrated Circuits (ASICs), FieldProgrammable Gate Arrays (FPGAs) circuits, any other type of integratedcircuit (IC), and/or a state machine.

A processor in association with software may be used to implement aradio frequency transceiver for use in a wireless transmit receive unit(WTRU), user equipment (UE), terminal, base station, radio networkcontroller (RNC), or any host computer. The WTRU may be used inconjunction with modules, implemented in hardware and/or software, suchas a camera, a video camera module, a videophone, a speakerphone, avibration device, a speaker, a microphone, a television transceiver, ahands free headset, a keyboard, a Bluetooth® module, a frequencymodulated (FM) radio unit, a liquid crystal display (LCD) display unit,an organic light-emitting diode (OLED) display unit, a digital musicplayer, a media player, a video game player module, an Internet browser,and/or any wireless local area network (WLAN) or Ultra Wide Band (UWB)module.

1. A dual mode wireless transmit/receive unit (WTRU) comprising: areceiver configured to receive global system for mobile (GSM)/enhanceddata rates for GSM evolution (EDGE) radio access network (GERAN) cellinformation while receiving wireless communications in a long termevolution (LTE)/evolved universal terrestrial radio access network(EUTRAN) cell; a processor configured to receive list of available cellsand their technologies in order to perform measurements on LTEfrequencies and GERAN frequencies to be used for a handover from asource LTE cell to other wireless coverage areas, including a targetGERAN cell using the GERAN cell information; and a transmitterconfigured to send a measurement report of the measurements on the GERANfrequencies to a source evolved Node B (eNB).
 2. The WTRU as in claim 1,further comprising a second receiver configured to receive GERANcommunications, where the receiver recognizes the target technology fromamong a plurality of radio access technologies that are supported,whereby the processor communicates the target channel ID to the secondreceiver.
 3. The WTRU as in claim 1, further comprising a secondtransmitter configured to start GERAN access procedures by sending apacket switched (PS) attach request to a target base station controller(T-BSC), wherein the second receiver is configured to receive a PSattach accept signal from the T-BSC.
 4. The WTRU as in claim 3 whereinthe second transmitter is configured to send a PS attach accept ACKsignal to the T-BSC.
 5. The WTRU as in claim 1, further comprising: asecond receiver configured to receive GERAN communications and toreceive a RAN mobility information signal from a target base stationcontroller; and a second transmitter configured to send GERANcommunications and to send a RAN mobility information ACK signal to thetarget base station controller.
 6. A source evolved Node B (eNB)comprising: a transmitter configured to send a measurement listincluding different radio access technologies, including GERAN, to awireless transmit/receive unit (WTRU); a receiver configured to receivea measurement report from the WTRU having measurements of a target GERANcell for a handover of the WTRU; and a processor configured to make adecision for handover of the WTRU from a source LTE cell to the targetGERAN cell based on the measurement report.
 7. The eNB as in claim 6,wherein the transmitter is configured to send a relocation request to asource mobility management entity (MME) supporting the source eNB, therequest having a target system ID and the source eNB ID.
 8. The eNB asin claim 6, wherein the receiver is configured to receive a relocationcommand that includes a temporary mobile subscriber identity (TMSI) anda target base station controller (T-BSC) ID, whereby the processor isconfigured to establish a temporary tunnel to the T-BSC to forward data.9. A source LTE mobility management entity (MME) comprising a processorconfigured to determine a handover target GERAN system for a handover ofa wireless transmit/receive unit (WTRU) from a received relocationrequest from a serving eNB, the relocation request having a source cellID and a target cell ID, the processor configured to identify a ServingGPRS Support Node (SGSN) that controls a target GERAN cell by mappingthe target GERAN Cell ID to an SGSN IP address.
 10. The MME as in claim9, wherein the processor is configured to forward a request for resourceallocation in the target system via a message that includes the targetcell ID and the WTRU ID as an international mobile subscriber identity(IMSI).
 11. The MME as in claim 9, wherein the processor is configuredto release the resources allocated to the WTRU in LTE system afterreceiving handover complete message from a target SGSN.
 12. A method forhandover of a dual mode wireless transmit/receive unit (WTRU) from along term evolution system cell to a global system for mobile(GSM)/enhanced data rates for GSM evolution (EDGE) radio access network(GERAN) cell, the method comprising: receiving GERAN cell informationwhile receiving wireless communications in a LTE cell; receiving a listof available cells and their technologies from the LTE system in orderto perform measurements on LTE frequencies and GERAN frequencies to beused for a handover from a source LTE cell to other wireless coverageareas, including a target GERAN cell using the GERAN cell information;and sending a measurement report of the measurements on the GERANfrequencies to a source evolved Node B (eNB).
 13. The method as in claim12, further comprising a first receiver of the dual mode WTRUrecognizing a target radio access technology from among a plurality ofsupported radio access technologies; and communicating a target channelID to a second receiver of the dual mode WTRU.
 14. The method as inclaim 12, further comprising starting GERAN access procedures by sendinga packet switched (PS) attach request to a target base stationcontroller (T-BSC), wherein the second receiver is configured to receivea PS attach accept signal from the T-BSC.
 15. The method as in claim 14,further comprising sending a PS attach accept ACK signal to the T-BSC.16. The method as in claim 12, further comprising: receiving a RANmobility information signal from a target base station controller; andsending a RAN mobility information ACK signal to the target base stationcontroller.
 17. A method for an evolved Node B (eNB) performing handoverof a wireless transmit/receive unit, comprising: sending a measurementlist including different radio access technologies, including GERAN, tothe wireless transmit/receive unit (WTRU); receiving a measurementreport from the WTRU having measurements of a target GERAN cell for thehandover; and performing a decision for handover of the WTRU from asource LTE cell to the target GERAN cell based on the measurementreport.
 18. The method as in claim 17, wherein the transmitter isconfigured to send a relocation request to a source mobility managemententity (MME) supporting the source eNB, the request having a targetsystem ID and the source eNB ID.
 19. The method as in claim 17, furthercomprising receiving a relocation command that includes a temporarymobile subscriber identity (TMSI) and a target base station controller(T-BSC) ID; and establishing a temporary tunnel to the T-BSC to forwarddata in response to the relocation command.